Precision clock synchronization protocol for substation automation
Dennis Holstein, Publisher
July 2002
When a utility's substation automation includes protection schemes over the
substation LAN, precision clock synchronization is needed. One approach is to
run a timing wire between IEDs to synchronize each IED clock. Another approach
is to synchronize the clocks using a multicast message over the substation LAN.
Earlier papers
In 1999 Bitronics wrote a paper (power point
presentation) describing an implementation for time synch over the
substation LAN. In 2000 Tor Skeie wrote and ABB paper describing ABB's research
to develop a scheme for synchronizing clocks over the substation LAN. The scheme
was used by IEC TC57 working groups to develop the protocol that is specified in
IEC 61850. John Tengdin wrote a series of papers in 2000 describing clock
synchronization, time tagging requirements,
and time
synch requirements for substation automation. To review these papers, click
on the highlighted text.
IEEE 1588
IEEE 1588 is in the final stages of approval. This standard defines a protocol enabling precise synchronization
of in measurement and control systems implemented with technologies such as
network communications, local computing and distributed objects.
IEEE 1588 will be
applicable to systems communicating by local area networks supporting multicast
messaging including but not limited to Ethernet. The protocol will enable heterogeneous
systems that include clocks of various inherent different precisions,
resolution, and stability to synchronize. The protocol will support system-wide
synchronization accuracy in the sub-microsecond range with minimal network and
local clock computing resources. The default behavior of the protocol will allow
simple systems to be installed and operated without requiring the administrative
attention of users.
IEEE 1588 is included as a normative reference in IEEE
P1525 (substation automation requirements using the Internet protocol suite),
which is a normative reference in IEEE PC37.115 (standard test method for
evaluating substation automation communication performance).
The dilemma
The requirement for clock synchronization is clearly stated. Implementation
using a master GPS clock and timing wire to distribute time to local clocks is
inexpensive and effective. But if the utility has implemented a substation
automation architecture that does not include a timing wire then we have a minor
dilemma: use IEC 61850 or use IEEE 1588.
OPUS recommendation
You can read both specifications and decide which is the best implementation.
OPUS recommends IEEE 1588.
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